1. Field of the Invention
The invention relates to a power converter suitable for an electric vehicle. More particularly, the invention relates to a power converter such as a voltage converter or an inverter that handles current to be supplied to a running motor of an electric vehicle. The term “electric vehicle” in this specification includes a fuel cell vehicle and a hybrid vehicle provided with both an electric motor and an engine.
2. Description of Related Art
A power converter such as an inverter or a converter is provided with a capacitor for smoothing input current or output current. The capacitor is an element that tends to generate heat, and the current supplied to the running motor of the electric vehicle is several tens of amperes, so this kind of capacitor that smooths current has a high capacity and also generates a large amount of heat. On the other hand, devices that are mounted in a vehicle must be compact. As a result of making the power converter smaller, the packaging density of the components increases, so it becomes important to not only cool the components, but also to reduce the effects of heat on other components. In particular, in addition to generating a large amount of heat itself, the capacitor itself is not very heat resistant, so it is important to protect the capacitor from the heat of other components.
Japanese Patent No. 4702311 and Japanese Patent Application Publication No. 2009-206342 (JP 2009-206342 A), for example, propose technology related to countermeasures against heat for capacitors. The technology described in Japanese Patent No. 4702311 protects a capacitor from heat generated by an inverter circuit or the like, by arranging a metal plate between the capacitor and an electronic component that generates heat. The metal plate reflects the heat generated by the electronic component. Also, the metal plate is fixed to a housing, so the heat absorbed by the metal plate is diffused to the housing. Thus, the metal plate protects the capacitor against heat. Further, in order to insulate the capacitor from surrounding components, the area around the capacitor is covered with resin. However, when the capacitor or an electrode provided extending from the capacitor contracts repeatedly due to repeated changes in temperature (a thermal cycle), repeated stress is applied to the resin, which may cause it to crack. Depending on the position and shape of the crack, current may flow from the capacitor to the metal plate through the crack, and as a result, insulation between the capacitor and other components may be unable to be ensured. JP 2009-206342 A proposes arranging a resin plate between the electrode and the filled resin to prevent the resin filled around the capacitor from cracking. The effects from expansion and contraction of the electrode are mitigated by this resin plate, so stress that acts on the filled resin is reduced.